UCL Participation in new ESA mission Euclid

6 October 2011

Astronomers in two departments at UCL – Mullard Space Science Laboratory and Physics & Astronomy, and across Europe are celebrating today with the official selection of the Euclid space mission by the European Space Agency (ESA). This new satellite will be launched at the end of this decade and will provide Hubble Space Telescope-quality images across the whole sky.

At the heart of Euclid is a massive optical digital camera - one of the largest such cameras put into space - and UCL astronomers are leading efforts to design and build this new instrument. "This camera can take pictures of the sky more than 100 times larger than the Hubble telescope can" comments Professor Mark Cropper of Mullard Space Science Lab, UCL, who is the leader of the optical camera team. "Each frame from our instrument is the equivalent of nearly 300 HDTV screens, and one arrives every 15 minutes" explains Cropper. “It will image half of the sky in six years, reaching out to the distant parts of the Universe”.

Dr Richard Cole, also of the Mullard Space Science Lab and project manager for the optical camera, says “UCL will be leading a consortium of research groups across four nations to design and build our instrument. Extremely high levels of performance will be needed from the detector electronics, to be built here at UCL, to achieve the science objectives of the mission.”

A key goal of Euclid and the VIS instrument is to capture light from distant galaxies and study their detailed shapes. Normal matter (atoms, and parts of atoms) makes up only about 5% of the Universe. We don’t know what the other 95% is. Some of it (20%) feels normal gravity, and we call it Dark Matter, but most of it (75%) is causing the expansion of the Universe to accelerate, and we call it Dark Energy. We’ve known this for less than 15 years. It’s now a high priority for science to understand what most of the Universe is made of.

Euclid will make exquisite measurements of the effects of Dark Energy and Dark Matter by taking pictures of the sky in red and infra-red light, and also by splitting the infra-red into its colours.

One technique is called gravitational lensing. Concentrations of matter bend light and distort the shape of distant galaxies. Because most of the matter in the Universe is Dark Matter, it is this that does most of the bending.

Even if the galaxies are randomly orientated on the sky, the bending will tend to stretch them in a preferred direction. The amount of stretching allows the matter to be mapped, even though we can’t see it directly. "Observations of Dark Matter are wonderful in themselves", comments Prof. Ofer Lahav of the Physics & Astronomy Department at UCL, "but even better is that Euclid can also see the effects of Dark Energy, a mysterious ingredient that was discovered only a decade ago and appears to be driving the accelerated expansion of our Universe". We can look back in time by imaging ever more distant galaxies, as light from them takes time to reach us. If we work out how the clumpiness of the matter has changed over time, then we can calculate the properties of Dark Energy, because it will have a different effect on the clumping depending on how it has caused the Universe to accelerate.

In another technique, called galaxy clustering, we can measure how the clumpiness of the Universe has grown directly. Maps of this clustering have been made using existing surveys, but Euclid will do this on a grand scale to very much greater distances. Because we can measure the distance of each galaxy from the infrared colours, again, comparing the clumping at different distances Euclid can measure how this clumping has grown over time. This provides an independent measure of the Dark Energy.

No-one yet knows what dark energy could be, but Euclid will bring us much closer to answering this mystery. Dr Filipe Abdalla, also from Physics & Astronomy, adds "Euclid will also measure the motions of tens of millions of galaxies and from that we can test the strength of gravity in the distant Universe. Any differences from the expected would indicate that our ignorance of gravity on cosmological scales is masquerading as Dark Energy.”

There are other techniques, too, almost as powerful, which add to the evidence. Astronomers and physicists believe that Euclid will revolutionise our knowledge of the Universe, from dark matter and dark energy, to weighing neutrinos.

Astronomers will also use the vast resource of Euclid images and colours to examine a myriad of other questions, such as how galaxies form and change over time. It will enlighten the life history of our own Milky Way galaxy. The Euclid dataset will be a treasure trove for astronomers for decades to come, allowing everyone to stare anywhere in the Cosmos with Hubble-like clarity.

How Euclid will be built

Euclid is a concept brought by European scientists to the European Space Agency in response to their Cosmic Vision call, in 2007. Since then it has been studied and developed by ESA, aerospace industry across Europe and by the Euclid scientific consortium itself, who will design and build the instruments and do the data processing.

Euclid should be launched in 2019. It is planned to operate the satellite for 7 years or more.

Beyond UCL, the UK has a strong presence in Euclid. UK science groups will be funded by the UK Space Agency.